Is there a fast way to make lamp brighter?
As suggested by @JachymMichal, Just keep the lamp section open on the properties window.
There is a good reason to keep intensity of the light as a completely separate control.
Intensity and lamp size are two very different qualities.
Scaling the light it will just change the quality of the shadow. A very smalll light source will give a very defined sharp shadow. A large source will yield softer less defined shadows.